ABSTRACT:Standard testing methods of MPI programs do not guarantee coverage of all non-deterministic interactions (e.g., wildcard-receives). Programs tested by these methods can have untested paths (bugs) that may become manifest unexpectedly. Previous formal dynamic verifiers cover the space of non-determinism but do not scale, even for small applications. We present DAMPI, the first dynamic analyzer for MPI programs that guarantees scalable coverage of the space of non-determinism through a decentralized algorithm based on Lamport-clocks. DAMPI computes alternative non-deterministic matches and enforces them in subsequent program replays. To avoid interleaving explosion, DAMPI employs heuristics to focus coverage to regions of interest. We show that DAMPI can detect deadlocks and resource-leaks in real applications. Our results on a wide range of applications using over a thousand processes, which is an order of magnitude larger than any previously reported results for MPI dynamic verification tools, demonstrate that DAMPI provides scalable, user-configurable testing coverage.